A conventionally known headup display device is mounted to a vehicle such as an automobile and displays information on a combiner to assist a driver.
One known example of such a headup display device includes, in addition to a display that emits display light relating to predetermined information and a mirror that reflects the display light emitted from the display toward a combiner, a transparent cover that prevents an object (such as trash or a coin) from entering the device (refer to, for example, PTL 1 or 2).